1. Field of the Invention
The present invention relates to a driving circuit configured to drive a vibration-type actuator.
2. Description of the Related Art
The vibration-type actuator is a non-electromagnetically driving actuator configured to generate a high-frequency vibration in an electro-mechanical energy conversion element such as a piezoelectric element by applying an alternating voltage to the electro-mechanical energy conversion element whereby vibration energy is output in the form of continuous mechanical motion. The vibration-type actuators are classified into a standing wave type and a traveling wave type according to types of generated vibrations.
FIG. 16 illustrates a conventional driving circuit configured to drive a vibration-type actuator of the traveling wave type (see Japanese Patent Publication No. 5016277). A vibration member 101 is a combination of a piezoelectric element and an elastic element. The piezoelectric element is applied with an alternating voltage via driving electrodes 101a and 101b. An oscillator 601 generates an alternating signal corresponding to a driving frequency. A switching circuit 602 operates such that a switching element in the switching circuit 602 turns on and off in accordance with the alternating signal supplied from the oscillator 601 thereby generating an alternating voltage. The switching circuit 602 is connected to a DC voltage source (not shown) such that the alternating voltage is generated from a DC voltage supplied from the DC voltage source.
The actuator shown in FIG. 16 employs a two-phase driving scheme. In this scheme, alternating voltages with different phases are provided from two parts of the driving circuit. These two parts of the driving circuit are similar except that the phase of an input alternating voltage is shifted by ±90° by a 90°-phase shifter 603. Therefore, the following explanation is given only for a part 604 that is one of these two parts.
The alternating voltage Vi output from the switching circuit 602 is applied to a primary coil 401a of a transformer 401, and stepped up by an amount corresponding to the turn ratio of the secondary coil 401b to the primary coil 401a of the transformer 401. The stepped-up alternating voltage Vo is passed through an inductor 102 connected in series to the secondary coil 401b of the transformer 401 to remove harmonic components from the waveform of the alternating voltage Vo. The resultant alternating voltage Vo is applied to the driving electrode 101a. In the actuator disclosed in Japanese Patent Publication No. 5016277, a capacitor 103 is connected to the primary coil 401a of the transformer 401 such that series resonance occurs between the capacitor 103 and the primary coil 401a whereby the frequency characteristic of the alternating voltage Vo has a peak. Note that the series resonance frequency of the series of the capacitor 103 and the primary coil 401a of the transformer 401 is set to be equal to the resonance frequency of the vibration member 101. This configuration makes it possible to adjust the alternating voltage Vo by controlling the driving frequency even when a change occurs in the resonance frequency of the vibration member 101, whereby it is possible to reduce the power consumption.